1. Field of the Invention
The present invention relates to a process for manufacturing an extruded drainage medium, more particularly to the manufacture of a multi-sectional subsoil porous drainage pipe for applications in the field of civil engineering.
2. Description of the Related Art
As shown in FIG. 1, a conventional porous drainage pipe is fabricated from thermoplastic resin by extruding molten resin material to form a plurality of strands 2 that travel downwardly after exiting the extruder 1. The strands 2 are led to a forming apparatus 3 for making a tubular preform 201. While passing through the forming apparatus 3, the strands 2 are in a plasticised or softened condition and are blown by a fluid of high velocity, so that the strands 2 will be entangled to form a matrix with sufficient structural strength and possessing water permeability after setting. The tubular matrix exiting the forming apparatus 3 will travel through a roll unit 4 to smoothen the outer diameter thereof, and will subsequently enter into a cooling tank (not shown) located below the roll unit 4.
Several disadvantages may be encountered in the above-described process for fabricating the porous drainage pipe. Particularly, when the preform 201 emerges from the tip rolls of the roll unit 4 and enters into the cooling tank, it becomes inflexible due to a sudden drop of temperature and forms a rigid pipe. Thus, the cooling tank must have a depth sufficient to receive a certain length of rigid pipe before cutting. Moreover, since the depth of the cooling tank is limited, the pipe has to be cut off after extending downward to a predetermined length.
An object of this invention is to provide a process for fabricating a subsoil porous drainage medium which is capable of being delivered easily from a cooling tank.
Another object of this invention is to provide a flexible, multi-sectional porous drainage medium consisting of a plurality of links connected by flexible necked-down sections which can be cut into pieces with a desired number of the links.
According to the present invention, there is provided a process for making a porous drainage medium. The process includes the steps of: extruding a molten thermoplastic resin material to form a plurality of strands; blowing the strands in a plasticised condition using a high-velocity fluid to entangle the strands while passing the strands through a forming device, so as to result in a preform consisting of entangled strands; pinching the preform to form necked-down sections at intervals along the length of the preform, thus providing a plurality of links interconnected by the necked-down sections; and cooling the preform having the necked-down sections to form the porous drainage medium.